A selection procedure for the rapid expression of carcinogen-induced malignant transformation of retrovirus-infected Fischer rat embryo cells

This study evaluates a procedure that accelerates the expression of the transformation of retrovirus-infected Fischer rat embryo cells. The endpoints used were anchorage-independent growth (formation of colonies in soft agarose) and formation of foci on a contact-inhibited monolayer. The cells were treated in monolayer with chemical, solvent (negative control) or medium alone for 3 days; then the chemical was removed and the cultures re-fed with medium alone for an additional 3 days. Cells in monolayer were disaggregated, suspended in liquid medium over solid agar for 4 days, disaggregated again and seeded into monolayer. After 2–4 wk without additional subculturing, cells from monolayer were seeded in soft agarose. Suspension of retrovirus-infected rat embryo cells above agar after chemical treatment resulted in rapid expression of neoplastic phenotypes. Cells treated in monolayer with the carcinogens, benzidine dichloride, dimethyl benzanthracene, 4,4-oxydianiline, 4-nitroquinoline- N-oxide and N-methyl- N′-nitro- N-nitrosoguanidine demonstrated colony formation in soft agarose or morphological transformation within 2–4 wk after being held in suspension for 4 days. In addition two carcinogens, benzo[ a]pyrene and N-2-acetylaminofluorene and two noncarcinogens, benzo[ e]pyrene and N-4-acetylaminofluorene did not induce neoplastic changes in this time period. The suspension technique may be a useful modification of this assay because it selectively amplifies neoplastic transformation after treatment with a number of chemicals.